Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/51

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41
Dr. Berger on the Isle of Man.

Third variety. Granular quartz forms the basis of it, in which are interspersed some small grains or nodules of transparent quartz, and some specks of white mica.

The Fourth and last variety, is a granular quartz over-run by veins of the same substance. There are in it but a few specks of mica.

The grey-wacke of St. Ann's-head is distinctly stratified, the planes of the strata being quite even, a mode of structure which originates from an accumulation of specks of mica, which render the rock readily fusible into a brown-greyish enamel, while it is infusible in those parts where the mica is wanting.

Along the shore between Kirk-michael and Peel-town, the grey-wacke is rather thick-slaty, traversed by slender and parallel veins of white quartz, coeval with the rock itself since they occur along the seams of stratification. The mean specific gravity of seven specimens of grey-wacke is 2.702.

C. Flœtz Rocks.

Limestone.

It would seem as if the appearance of the limestone was connected with the absence of the exterior line of mountains on the eastern side of the South Group. We trace it from Cass-ny-Hawin River to Purl-Keill-Moirrey (Langness-point excepted) but it never reaches to any elevation on the slope of the mountains; it is confined to the shore or its vicinity.

It lies conformably over the most superficial of the produced strata of grey-wacke, but the dip becomes less as the strata retreat farther back from the land into the sea. It may be comprehended between 10° and 20°.


Vol. II.F